A Novel Vanadium-Titanium Redox Flow Battery with Mixed Electrolyte Approach

Abstract

Redox flow batteries (RFBs) enable independent scaling of energy and power, making them a suitable candidate for the grid-scale energy storage solutions. However, the market is currently dominated with vanadium RFBs which are prone to extreme price volatility. To reduce the inherent material costs while retaining the efficiencies, the study investigates a novel vanadium-titanium RFB using (i) a separate, acid-based system (V 2 O 5 + H 2 SO 4 catholyte, and TiCl 3 + HCl anolyte); (system-1), (ii) a premixed acid-based electrolyte at 0% state of charge (system-2), and (iii) an ionic-liquid based premixed electrolyte comprising [Bmim]Cl + VCl 3 , and its titanium counterpart (system-3). Several physical, and electrochemical characterizations were performed, such as viscosity, and density from 298-333 K, cyclic voltammetry tests, and electrochemical impedance spectroscopy to establish a stable redox window for V(IV/V), and Ti(III/IV) in the presence of an ionic-liquid. In galvanostatic cycling with a SPEEK membrane, system-1 delivers coulombic efficiency (CE) greater than 98%, at 10-20 mAcm -2 ; with an energy density of 24.53 Wh L -1 . System-2 (premixed acid) retains the CE%, while the voltage efficiency (VE) drops by 10%. The results demonstrated that premixing at 0% SOC effectively limits the crossover in V-Ti RFBs, while optimization of proton donors, and the inclusion of additives is necessary to enhance the nominal discharge potential, and thereby effectively deploying in the grid-scale.